Halogenated hydrocarbons containing chlorine as well as fluorine have been widely used as refrigerants, propellants, cleaning agents, etc., because of their many remarkable properties such as extremely high chemical stability and physiological inactivity. Useful compositions including such compounds have included R501 (a mixture of CCl.sub.2 F.sub.2 and CHClF.sub.2) and R502 (a mixture of CHClF.sub.2 and CClF.sub.2 CF.sub.3). In recent years there have been concerns over the impact of these chlorine-containing materials on the atmosphere and the environment, and wide-ranging restrictions have been put on their production and use. Accordingly, there has been recent interest in processes which dispose of various halogenated hydrocarbons containing chlorine. One method for their destruction is incineration. However, this method is energy intensive and often produces additional wastes which need to be treated before disposal into the environment. Another method for their disposal involves their catalytic decomposition to mixtures comprising hydrogen chloride, hydrogen fluoride and carbon dioxide (see, e.g., U.S. Pat. No. 5,118,492).
The hydrofluorocarbons difluoromethane (i.e., CH.sub.2 F.sub.2 or HFC-32) and 1,1,1,2-tetrafluoroethane (i.e., CH.sub.2 FCF.sub.3 or HFC-134a) have been proposed as a replacement for some chlorofluorocarbons (CFCs), particularly, in refrigeration, air-conditioning and other applications (see, e.g., European Patent Publication No. 508,660 A1 and U.S. Pat. Nos. 4,861,744 and 5,114,544). Compositions containing HFC-32, HFC-134a and 1,1,2,2-tetrafluoroethane (i.e., CHF.sub.2 CHF.sub.2 or HFC-134) have been found useful as refrigerants, heat transfer media, foam expansion agents, aerosol propellants, solvents and power cycle working fluids (see, e.g., PCT Patent Publication No. WO 93/09199). Compositions containing HFC-32, HFC-134a and/or HFC-134 and pentafluoroethane (i.e., CHF.sub.2 CF.sub.3, HFC-125) have also been found useful for the same applications as those listed above (see, e.g., U.S. Pat. No. 5,185,094). Accordingly, there is interest in developing efficient processes for the production of the hydrofluorocarbons, HFC-32, HFC-134a, HFC-134, HFC-125 and mixtures thereof. It is evident that methods for converting halogenated hydrocarbons containing chlorine into useful hydrofluoroalkanes would not only remove compounds considered harmful to the environment but in turn would also afford materials, which can be used for refrigerants, propellants, etc., and also have a benign effect on the environment.
Hydrogenolysis is a known method for reducing the chlorine and/or bromine content of halogenated hydrocarbons. For example, U.K. Patent Publication No. 1,578,933 discloses a process for the hydrogenolysis of certain starting materials to tetrafluoroethane using a hydrogenation catalyst (e.g., palladium supported on alumina or carbon). These starting materials are haloethanes containing four or five fluorine atoms. When the organic starting material is CF.sub.3 CCl.sub.2 F (CFC-114a), CF.sub.3 CH.sub.2 F (HFC-134a) is obtained almost to the exclusion of CHF.sub.2 CHF.sub.2 (HFC-134); and when the organic starting material is CClF.sub.2 CClF.sub.2 (CFC-114) the reaction product usually comprises a mixture of the two tetrafluoroethane isomers. Hydrogenolysis of certain fluorochlorocarbons using tube reactors made of various materials has been disclosed. For example, U.S. Pat. No. 2,615,926 discloses use of platinum tubes, U.S. Pat. No. 2,704,775 discloses use of nickel and stainless steel tubes and U.S. Pat. No. 3,042,727 discloses use of a Vycor.RTM. tube. U.S. Pat. No. 5,208,397 discloses the hydrogenolysis of halocarbon mixtures in reactors of silicon carbide and/or a metal selected from aluminum, molybdenum, titanium, nickel, iron or cobalt (or their alloys).